In a long term evolution (LTE) system in the 3GPP standardization organization, each radio frame is 10 ms in length and equally divided into ten subframes. As shown in FIG. 1, taking an FDD system as an example, each radio frame is 10 ms in length and contains ten subframes each of which is 1 ms in length. Each subframe consists of two successive time slots which are 0.5 ms in length. That is, the kth subframe contains a time slot 2k and a time slot 2k+1. One downlink transmission time interval (TTI) is defined on one subframe.
FIG. 2 shows the structure of a downlink subframe in an LTE system. In this structure, the first n OFDM symbols (n is 1, 2 or 3) form a downlink control channel region, and are used for transmitting user downlink control information, including a physical control format indication channel (PCFICH), a physical HARQ indication channel (PHICH), and a physical downlink control channel (PDCCH); and the remaining OFDM symbols are used for transmitting a physical downlink shared channel (PDSCH) and an enhanced PDCCH (EPDCCH). A downlink physical channel is a set of a series of resource elements (REs). RE is the minimum unit of time-frequency resources, that is, in terms of frequency, it is one sub-carrier, while in terms of time, it is one OFDM symbol. The allocation granularity of physical resources is physical resource block (PRB). One PRB contains twelve successive sub-carriers in terms of frequency and corresponds to one time slot in terms of time. Two PRBs within two time slots on a same sub-carrier within one subframe are called a PRB pair. Different REs can be used for different functions, for example, cell-specific reference signal (CRS), user-specific demodulation reference signal (DMRS), and channel state indication-reference signal (CSI-RS). Specifically, in one subframe, there can be at most forty REs used for CSI-RS. The base station can configure some or all of those REs actually for CSI-RS.
Depending upon the number of antennas deployed in the base station, one, two, four or eight ports for CSI-RS can be configured. In order to determine time-frequency resources for CSI-RS resource mapping, it is necessary to indicate the period of CSI-RS, subframe offset and REs in one subframe, wherein CSI-RS subframe configuration is used for indicating the position of a subframe occupied by the CSI-RS, that is, indicating the period of CSI-RS and subframe offset; and the CSI-RS configuration is used for indicating REs occupied by the CSI-RS in one PRB.
In order to further improve the spectrum efficiency, data of a plurality of users can be multiplexed in power domain. Generally, the multiplexed users have different transmission power. In receiving data of such multiplexed users with high power, signals of users with low power can be processed by regarding them as noise, or also can be processed by other more advanced methods. In receiving data of such multiplexed users with low power, data of users with high power can be received first, and signals of users with high power are restored and deleted; and then, data of users with low power can be decoded. Here, data of a plurality of users can be multiplexed in same time, frequency and spatial resources so that users are distinguished merely depending upon different power; or, the above-mentioned time, frequency and spatial multiplexing method can be combined with power domain multiplexing to maximize the performance. How to effectively support multi-user multiplexing based on power domain is a problem to be solved.